Process and apparatus for molding composite articles

ABSTRACT

A method and an apparatus for molding composite articles are disclosed. The method generally involves the saturation of reinforcing fibers (e.g. glass fibers, carbon fibers, etc.) with a matrix (e.g. resin, epoxy, cyanate ester, vinyl ester, polyester, etc.) in/on a mold using a conventional resin transfer molding (“RTM”) process (e.g. “RTM-light”) or a vacuum assisted resin transfer molding (“VARTM”) process (e.g. advanced VARTM or “A-VARTM”), and, once saturation is completed, the vibration of the matrix-infused fibers using controlled ultrasonic sound waves transmitted through the mold. By vibrating the matrix-infused fibers with the ultrasonic sound waves, the method and apparatus allow voids present between fibers to be closed and localized pockets of gases to be dislodged and degassed, and also allow the fibers to compact, thereby producing composite articles with reduced porosity and higher compaction.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present patent application claims the benefits of priority of U.S.Provisional Patent Application No. 61/561,521, entitled “Apparatus andMethod for the Controlled Ultrasonic Resin Infusion of CompositeArticles” and filed at the United States Patent and Trademark Office onNov. 18, 2011, the content of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention generally relates to the field of resin transfermolding (“RTM”) processes and vacuum assisted resin transfer molding(“VARTM”) processes used for molding composite articles, and moreparticularly relates to advanced vacuum assisted resin transfer molding(“A-VARTM”) processes.

BACKGROUND OF THE INVENTION

There are many industries producing fiber-reinforced resin compositeparts. For instance, composite parts are commonly used in theautomotive, marine, industrial, and aerospace industries.

Depending on the requirements of each industry, various methods andprocesses can be used to produce composite parts. One commonly knownmethod is the resin transfer molding (“RTM”) process in whichreinforcing materials (e.g. glass fibers, carbon fibers, etc.) areplaced into a closed mold and then impregnated at high pressure (e.g.400 psi and higher) with a liquid matrix (e.g. a polymer resin). In avariant of the RTM process, the closed mold is put under vacuum prior tothe injection, at atmospheric pressure, of the matrix to impregnate thereinforcing materials. Such a process is generally known as a vacuumassisted resin transfer molding (“LIGHT RTM”) or (“VARTM”) process. Inline with the VARTM process is the advanced VARTM (“A-VARTM”) process.In A-VARTM process, the mold is usually open and light weight comparedto other RTM or VARTM processes. To compress the layers of reinforcementmaterials on a complex mold shape, a flexible vacuum bag is used. Whenthe bag is put under vacuum, the atmospheric pressure insures the propercompaction of the reinforcing materials and removes air in the bag.After impregnation of the reinforcing fibers with the matrix, thepressure on the bag becomes neutral and degassing become difficult.

One of the problems of composite parts made from VARTM processes is theporosity. Indeed, despite due care, the impregnation of the reinforcingmaterials with the matrix is never perfect and the resulting compositepart typically contains porosities such as voids and gas bubbles aroundfibers and in the matrix. Though porosities are generally not a majorproblem in the automotive and marine industries, they are a significantproblem for the aerospace industry. Indeed, in the aerospace industry,the porosity content of a composite part must be severely controlled toprevent its failure.

Unfortunately, current RTM, VARTM, even A-VARTM processes are not ableto produce composite parts with the requisite limited amount ofporosities suitable for the aerospace market.

To overcome the shortcomings of VARTM processes, the aerospace industrycurrently produces composite parts using a specific process, sometimesreferred to as pre-preg, using reinforcing materials pre-impregnatedwith a resin matrix and ready to be vacuum bagged and cured at hightemperature (e.g. 130° C. and higher) in a pressurized autoclave. Themain advantage of autoclaved pre-impregnated composite parts is thealmost complete absence of voids and porosities (typically less than1%). However, the pre-impregnated process is excessively expensive. Forinstance, pre-impregnated reinforcing materials must be stored at −18°C. or colder to slowdown the cure cycle of pre-mixed resin, they have tobe thawed many hours before usage and they need significant supervision.In addition, the pre-impregnated process requires a pressurizedautoclave which is very expensive, particularly for large compositesparts.

Hence, there is a need for an improved A-VARTM process and associatedmolding apparatus which could mitigate at least some shortcomings ofprior art VARTM processes and which could be able to produce compositeparts and articles with a porosity level similar or better to thepre-impregnated process.

SUMMARY OF THE INVENTION

The shortcomings of prior art methods and processes for moldingcomposite articles using RTM, VARTM, or A-VARTM processes are at leastmitigated by submitting the resin-infused reinforcing materials toultrasonic sound waves.

Hence, a typical process to produce resin-infused composite articles inaccordance with the principles of the present invention generallycomprises the placement of reinforcing materials (e.g. glass fibers,carbon fibers, etc.) in or on a mold, the infusion, typically undervacuum, of the reinforcing materials with a matrix (e.g. a resin), and,once the infusion is completed and before the end of gel time, thetransmission of controlled ultrasonic sound waves to the resin-infusedreinforcing materials through the mold.

For its part, a molding apparatus in accordance with the principles ofthe present invention generally comprises a mold having a moldingsurface, and an infusion vacuum bag configured to cover the reinforcingmaterials during the infusion and apply pressure thereon. In accordancewith the principles of the present invention, the mold comprises atleast one though typically several ultrasound transducers mounted to themold and/or embedded within its thickness.

The ultrasonic sound waves are used to vibrate the reinforcing materialsvia the mold when their reinforcing fibers are saturated with resin. Byvibrating the reinforcing materials, it is possible to eliminate or atleast significantly reduce voids and bubbles present in and around theresin-infused reinforcing materials and thereby reduce the level ofporosity in the final molded composite article and getting a bettercompaction of the fibers.

Since RTM, VARTM, A-VARTM processes can be used with different types ofpolymer resin matrices, reinforcing materials, and molds, the mold willtypically comprises different ultrasonic transducers typically able tooperate at different frequency ranges. The choice of the ultrasonictransducers will typically be based on the type of matrices andreinforcing materials used, and on the mold types and shapes. Inaddition, the position of each of the transducers on or embedded in themold is typically determined to provide proper vibration of theresin-infused reinforcing materials.

In typical yet non-limitative embodiments, various ultrasonic frequencyranges are used to vibrate the resin-infused reinforcing materials. Insome of these embodiments, the different ultrasonic frequency ranges canbe transmitted at different times according to a predetermined sequence,and/or at different levels of power. For instance, high frequencyultrasonic sound waves (e.g. 170 kHz to 200 kHz, at 25 W) could betransmitted to generally vibrate the reinforcing fibers and thus closevoids present between fibers, followed, or preceded, by low frequencyultrasonic sound waves (e.g. 27 kHz to 40 kHz, at 25 W) to fill and/orfraction bubbles present in the resin. Other ultrasonic frequencies canhowever be used.

In typical yet non-limitative embodiments, the vacuum bag of the moldingapparatus comprises additional degassing vacuum ports strategicallypositioned on the bag (depending on the shape and size of the mold) formaximizing local degassing and specific bleeding of matrix used in theprocess.

Notably, the process and related molding apparatus in accordance withthe principles of the present invention allow the molding of compositearticles and parts having a much higher compaction of fibers due to thevibration of the reinforcing fibers when saturation is completed, i.e.when the reinforcing material fibers are wet (notably, dry fibers woulddamp vibrations and not provide results). Using such a process and itsrelated molding apparatus, the ratio matrix/fibers potential (e.g. 70%and higher) can be very high without creating dry spots, allowing themanufacturing of composite articles and parts which meet the stringentporosity level and high ratio of matrix/reinforcement fiber of theaerospace industry at a much lower cost than pre-impregnated or pre-pregprocesses.

Other and further aspects and advantages of the present invention willbe obvious upon an understanding of the illustrative embodiments aboutto be described or will be indicated in the appended claims, and variousadvantages not referred to herein will occur to one skilled in the artupon employment of the invention in practice. The features of thepresent invention which are believed to be novel are set forth withparticularity in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the inventionwill become more readily apparent from the following description,reference being made to the accompanying drawings in which:

FIG. 1 is schematic flow-chart of a process for molding compositearticles in accordance with the principles of the present invention.

FIG. 2 is a cross-sectional side view of a molding apparatus for moldingcomposite articles in accordance with the principles of the presentinvention.

FIG. 2A is an enlarged partial cross-sectional side view of the moldingapparatus of FIG. 2.

FIG. 3 is a cross-sectional side view of the mold of the moldingapparatus of FIG. 2, mounted to a support frame.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A novel process and related apparatus for molding composite articleswill be described hereinafter. Although the invention is described interms of specific illustrative embodiments, it is to be understood thatthe embodiments described herein are by way of example only and that thescope of the invention is not intended to be limited thereby.

Referring first to FIG. 1, a flow-chart depicting an embodiment of aprocess 100 to mold composite articles in accordance with the principlesof the present invention is shown.

In the present embodiment, the process 100 is mostly based on a A-VARTMprocess. Hence, the process 100 typically comprises the placement ofreinforcing materials on a mold which is in the shape of the desiredarticle (at 102). In the present embodiment, several types ofreinforcing materials can be used. For instance, glass fibers, carbonfibers, glass fiber fabric, carbon fiber fabric, etc.

Next, once the reinforcing materials are properly positioned on themold, a vacuum bag (or vacuum film) is disposed over the reinforcingmaterials, a vacuum pump is connected to the vacuum port of the bag anda matrix source is connected to the matrix port (at 104). At this point,the molding apparatus is ready for the injection of the matrix.

Then, the vacuum pump is turned on to create a full vacuum (e.g. ˜25 inHg or higher) in the vacuum bag. Understandably, as the vacuum iscreated inside the vacuum bag, atmospheric pressure will press the bagagainst the reinforcing material. At the same time, the resin matrix isintroduced into the bag via the matrix port for infusing the reinforcingmaterials (at 106).

Understandably, as the matrix is introduced in the bag under vacuum, thematrix will tend to fill most of the empty areas and voids in and aroundthe reinforcing materials.

Once the reinforcing materials is properly infused and saturated withresin, ultrasonic sound waves are transmitted to the resin-infusedreinforcing materials (also referred to as a laminate) through the mold(at 108). Some of the high-frequency ultrasonic sound waves will causethe vibration of the fibers of the reinforcing materials, allowing voidswhich naturally occur between fibers to be closed, thereby increasingthe overall the compaction of the laminate. Also, some low-frequencyultrasonic sound waves will cause gas bubbles to be filled-up and/orfractioned to be ultimately degassed by the vacuum and degassingport(s).

As it will be described in more details below, in the presentembodiment, the ultrasonic sound waves can be transmitted at differentfrequencies and/or power levels according to one or more predeterminedsequences.

After the transmission of the ultrasonic sound waves, the laminate isleft to cure at room temperature for a predetermined amount of time (at110). In the present embodiment, the curing of the laminate is performedunder vacuum.

Optionally, the laminate can be subjected to a high-temperature postcure to generally improve the thermal and mechanical properties of thelaminate (at 112).

Finally, the laminate is demolded and trimmed or machined to removeexcess materials and/or other surface imperfections (at 114). Thelaminate is then a finished composite article or part.

Referring now to FIGS. 2 and 2A, an embodiment of a molding apparatus200 to enable the molding process is depicted. The apparatus 200typically comprises a mold 210, typically made of composite material ormetallic material, and a vacuum bag 230 typically made from a thinsilicone membrane or nylon bagging film (e.g. Airtech Wrightlon 5400).

In the present embodiment, to provide a uniform rough surface finish onthe bag side of the molded composite part, a nylon peel ply 240 (e.g.Airtech econostitch) is disposed over the reinforcing materials 302prior to the installation of the vacuum bag 230. Also, in the presentembodiment, an infusion media layer 250 (e.g. Airtech green flow 75) isdisposed between the peel ply 240 and the vacuum bag 230 to allow theresin matrix to freely flow during its injection (see FIG. 2A).

As shown in FIG. 2, the mold 210 comprises a top surface 212 and abottom surface 214 defining a thickness 216. The top surface 212provides a molding surface for receiving the reinforcing materials 302.Understandably, the top surface 212 of the mold 210 is generally in theshape of the article or part to be molded. Hence, the top surface 212 isshown as flat for illustration purpose only.

For its part, the vacuum bag 230 comprises at least one resin inlet port232 allowing the resin to enter in the bag 230 during the infusion ofthe reinforcing materials 302, and at least one vacuum outlet port 234allowing a vacuum to be created inside the bag 230 prior and during theinfusion. The vacuum outlet port 234 is typically connected to a vacuumsource (e.g. ˜25 in Hg or higher) such as a vacuum pump (not shown).Understandably, when a vacuum is created inside the bag 230 which ismade from flexible material, the bag 230 collapses and applies pressureon the resin-infused reinforcing materials 302.

To allow the removal of air and other gas bubbles around the fibers andfrom the resin-infused reinforcing materials 302, the vacuum bag 230comprises at least one though typically several degassing vacuum outletports 236. Typically, these degassing vacuum outlet ports 236 arestrategically positioned on the vacuum bag 230 to provide properdegassing of the resin-infused reinforcing materials 302. Localdegassing ports allow to degas specific area(s) or region(s) and alsoallow to bleed extra matrix at specific location(s) to reach a maximumof fiber volume fraction (ratio fiber/resin) without creating dry spots.

To prevent the vacuum bag 230 from leaving a shinny finish and/or fromadhering on the resin-infused reinforcing materials 302 during themolding process, the layer of peel ply cloth 240 is disposed onreinforcement material 302 between the media fusion layer 250 andresin-infused reinforcing materials 302. This cloth 240 is typicallyremoved once the cure and/or post cure of the part is completed.

Also shown in FIG. 2, in accordance with the principles of the presentinvention, the mold 210 comprises at least one ultrasonic sound wavetransducer 218 mounted to its bottom surface 214 or embedded into itsthickness 216. In FIG. 2, two transducers 218 are shown. Embeddedtransducers such as transducer 218A are typically used for thincomposite parts (e.g. ˜0.0125″) whereas surface-mounted transducers suchas transducer 218B are typically used for thicker composite parts (e.g.0.0125″ up to 0.500″).

Embedded transducers are typically piezoelectric transducers made ofceramic flat disk. Such transducers are typically custom made by APCInternational, Ltd.

Surface-mounted transducers are typically Langevin type transducers.Such transducers are typically made of an aluminum base and a head madeof two bonded piezo-disks. Such transducers are made, for instance, byCleaning Technologies Group (Blackstone-NEY Ultrasonics).

As shown in FIG. 2, in the present embodiment of the molding apparatus200, the region 222 of the bottom surface 214 located underneath theembedded transducer 218A is made thicker. By making the region 218thicker (typically about the thickness of the transducer 218A), thevibrations 205 generated by the transducer 218A which travel downwardlyand away from the resin-infused reinforcing materials 302, are at leastpartially reflected back toward the resin-infused reinforcing materials.Hence, the thicker region 222 typically reduces energy losses.

Also, in the present embodiment of the molding apparatus 200, thesurface-mounted transducer 218B is mounted (e.g. bond or bolted) to ametallic plate 224 (e.g. an aluminum plate) itself mounted to the bottomsurface 214 of the mold 210. Such plate 224 is used to avoid themounting of the transducer directly to the mold 210 and to allow theeasy replacement of the transducer 218B if necessary. In addition, in amanner similar to region 222, the region 226 around the plate 224 isalso typically made thicker (about the thickness of the plate 224).

Understandably, the transducers 218 are connected to an ultrasoundgenerator (not shown). An ultrasound generator that has providedsatisfactory results is the Multisonic 40-80-120-140-170-220-270-MSG2-12t2-230V made by Blackstone-NEY Ultrasonics.

To promote the vibration of the fibers of the reinforcing materials andto allow the bubbles to collapse or fraction, sequences of ultrasoundsare typically transmitted.

An exemplary sequence that has shown satisfactory results is a follows:40 kHz for about 15 seconds, 170 kHz for about 15 seconds, 40 kHz forabout 10 seconds, 200 kHz for about 5 seconds, 170 kHz for about 15seconds, and so on as needed. Understandably, different resin matrix,reinforcing materials and mold shapes might warrant different sequences,different duration, different power levels and/or different frequencies.

When high frequencies are used (e.g. 170 kHz to 200 kHz), the heatproduced by the vibration of the fibers has shown to reduce the gel timesignificantly if used too often (e.g. for more than 60 secondsstraight). Depending on the matrix and reinforcing materials used,frequency sequences and time exposure will change.

Since the ultrasonic sound waves transmitted to the resin-infusedreinforcing materials are effectively transmitted through the mold 210,it is advantageous to have the mold 210 able to freely vibrate in orderto benefit, among other things, from constructive interferences betweenthe main vibrations and the returning ones. Using constructiveinterferences can allow the use less powerful sources of ultrasounds. Toallow the mold 210 to vibrate, it can be suspended on a frame 260 viapassive suspension elastomeric vibration isolator 262 (e.g. NewportVibration-Isolator). FIG. 3 shows an example of the mold 210 suspendedon the frame 260 via the suspensions (or isolators) 262. For a range ofultrasounds frequencies of 40 to 200 kHz, it has been found that thesuspension 262 can be also made of a hard rubber, e.g. of 50 to 70 Shoreor can be a mini air suspension.

In the present embodiment, the edges 220 of the mold 210 are thickerthan the thickness 216 of the mold 210, typically about twice as thick.The thicker edges 220 allow the vibrations moving outwardly to bereflected back inwardly, thereby preventing or at least reducing energylosses.

When the mold 210 vibrates, standing waves will likely occur and havethe advantage of high amplitude resulting from constructiveinterferences. However, the stationary status of these standing wavescan also create patterns of porosity since some regions of theresin-infused reinforcing materials 302 may vibrate more, or less, thanother regions.

In order to prevent stationary standing waves, displacement of thestanding waves can be achieved by a sweeping frequencies produced by theultrasound generator. For instance, sweeping lower frequencies will helpmove the standing waves by creating disturbance.

Typically, the ultrasonic sound waves will not shake the mold 210 butwill travel through the mold 210 and only vibrate the resin-infusedreinforcing materials 302. Notably, it has been found that the amount ofpower needed to properly vibrate the resin-infused reinforcing materials302 will be lowered if the vibrations are chosen to match the naturalresonance frequency of the mold 210. If the vibrations are not chosen tomatch the natural resonance frequency of the mold 210, more power may benecessary and the performances would possibly be affected.

The natural resonance frequency of the mold 210 can be obtained viadifferent methods. One method involves the use of a laserinterferometer. In such method, the mold 210 is suspended and thenknocked at the location where the transducer 218 is intended to beinstalled. Then the mold 210 is let vibrating and the vibration patternis measured with the interferometer. The position of the transducer 218can then be fine-tuned in order to obtain the desired vibration pattern.The method is then repeated for each transducer 218 to obtain propermatch and coverage performances.

With the proper equipment selected and installed on the moldingapparatus, the process will provide satisfactory results.

Below is an example of a process performed in accordance with theprinciples of the present invention.

First, the mold surface is prepared with a liquid release agent (e.g.Zyvax) and vacuum bag sealant tape (e.g. Airtech AT200Y) is applied onthe flanges of the mold.

Then, the reinforcing material plies are laid-up directly on the moldsurface and the peel ply layer, the media infusion layer and the vacuumbag are sequentially disposed over the reinforcing material plies. Thevacuum bag is connected to the resin matrix source and to the vacuumpump.

Then, the vacuum pump is turned on to create the vacuum inside thevacuum bag. Several checks are typically performed to make sure thatthere are no leaks.

At this point, the resin matrix is injected into the mold via the vacuumbag to infuse the reinforcing material plies. As soon as the reinforcingmaterial plies are thoroughly saturated with resin matrix, thetransmission of ultrasonic sound waves is started.

At first, low frequency ultrasounds (e.g. about 40 kHz) and highfrequency ultrasounds (e.g. about 170 kHz-200 kHz should be the maximumrange) are alternatively transmitted for about 10 to 15 seconds each tochase voids and bubbles. During the transmission of the ultrasounds,larger bubbles are going to surface and be degassed while microscopicbubbles are going to be fractioned into still smaller bubbles or willagglutinated together into larger bubbles and be degassed.

At this point, one or more of the degassing ports are slightly opened toallow localized zone(s) (e.g. sharp corners) to evacuate gases. However,it is important to prevent the resin matrix to flow into the degassingports.

Once the resin matrix no longer shows signs of degassing, the ultrasoundtransmission cycle is modified so that the high frequency ultrasounds(e.g. about 170 kHz) are transmitted for a longer period, about 15 to 25seconds, and the low frequency ultrasounds (e.g. about 40 kHz) aretransmitted for a shorter period of time, about 5 to 10 seconds.

The modified cycle is used to vibrate the fibers of the reinforcingmaterial plies and keep degassing. In that sense, there will typicallybe traces of degassing at the surface of the resin matrix when thefibers move and compact and cause microscopic bubbles surrounding thefibers to detach.

Then, again, one or more of the degassing ports are slightly opened toallow the evacuation of the gases. When the degassing ports are opened,it is important to prevent the resin matrix to flow in them.

When the degassing is completed, the resin matrix can be bled if needed.To do so, the degassing vacuum ports are gently opened to allow someresin matrix to fill the tubes (about 1% of the total extra resinmatrix) and then closed to allow the resin matrix to flow in dryer spotsand equilibrate. This operation can be repeated as needed. Notably, theamount of extra matrix allowed in the degassing vacuum ports tubesshould be calculated at the beginning of the infusion process andcollected in the tubes or in a catch pot if the quantity is large. Theresin matrix should be left to equilibrate for a period of time (e.g. 30seconds) after the last bleeding cycle before turning off theultrasounds.

Understandably, the matrix used in the above process should have a longenough gel time to allow the different steps of the process to beperformed properly. In that sense, when the fibers of the reinforcingmaterial plies vibrate because of the ultrasounds, they absorb animportant quantity of energy which is released in part as heat. Thisheat can cause the gel time of the matrix to be affected, sometimessignificantly.

Notably, once the gelation of the resin matrix has begun, thetransmission of ultrasounds shall stop to prevent irreversible fracturesof the matrix and/or of the reinforcement fibers. Understandably, ahardened matrix will resist vibrations and could present microfragmentations which will affect the structural integrity of thefinished composite article or part.

Once the process is well controlled, some steps could be made with theassistance of a computer.

By using a molding apparatus and executing a process in accordance withthe principles of the present invention, it is possible to eliminate orat least significantly reduce the void content and porosity while thematrix is in liquid phase. Composite parts and articles made with amolding apparatus and a process in accordance with the principles of thepresent invention are of very high quality (e.g. aerospace-grade) andcan compare with composite parts and articles made using prepreg in anautoclave.

While illustrative and presently preferred embodiments of the inventionhave been described in detail hereinabove, it is to be understood thatthe inventive concepts may be otherwise variously embodied and employedand that the appended claims are intended to be construed to includesuch variations except insofar as limited by the prior art.

The invention claimed is:
 1. A process for molding a composite article,the process comprising: placing reinforcing materials in or on a mold;infusing the reinforcing materials with a matrix until thematrix-infused reinforcing materials are saturated with the matrix;starting transmitting ultrasounds to the matrix-infused reinforcingmaterials when the matrix-infused reinforcing materials are saturatedwith the matrix, wherein the ultrasounds comprise ultrasounds in a firstrange of frequencies and ultrasounds in a second range of frequenciesthan the first range of frequencies; stopping transmitting ultrasoundsto the matrix-infused reinforcing materials before the matrix beginsgelation.
 2. The process as claimed in claim 1, wherein the ultrasoundsin the first range of frequencies and the ultrasounds in the secondrange of frequencies are transmitted according to a predeterminedsequence.
 3. The process as claimed in claim 1, wherein the ultrasoundsare transmitted through the mold.
 4. The process as claimed in claim 1,wherein the mold comprises at least one ultrasound transducer mountedthereto or embedded therein.
 5. The process as claimed in claim 1,wherein the process further comprises placing the reinforcing materialsunder vacuum prior to infusing the reinforcing materials with thematrix.
 6. The process as claimed in claim 1, wherein the processfurther comprises placing a vacuum bag over the reinforcing materialsand creating a vacuum between the vacuum bag and the mold.
 7. Theprocess as claimed in claim 6, wherein a peel ply layer is placedbetween the reinforcing materials and the vacuum bag.
 8. The process asclaimed in claim 7, wherein an infusion media layer is placed betweenthe peel ply layer and the vacuum bag.
 9. The process as claimed inclaim 6, wherein the process further comprises degassing at least oneregion of the matrix-infused reinforcing materials via at least onedegassing port located on the vacuum bag.
 10. The process as claimed inclaim 6, wherein the process further comprises degassing several regionsof the matrix-infused reinforcing materials via several degassing portslocated on the vacuum bag.
 11. A vacuum assisted resin transfer moldingprocess for molding a composite article in a mold, the processcomprising: placing reinforcing materials in or on the mold; while thereinforcing materials are under vacuum: infusing the reinforcingmaterials with a resin until the resin-infused reinforcing materials aresaturated with the resin; starting transmitting ultrasounds to theresin-infused reinforcing materials when the resin-infused reinforcingmaterials are saturated with the resin, wherein the ultrasounds compriseultrasounds in a first range of frequencies and ultrasounds in range offrequencies higher then the flat range of frequencies; stoppingtransmitting ultrasounds to the resin-infused reinforcing materialsbefore the resin begins gelation.
 12. The vacuum-assisted resin transfermolding process as claimed in claim 11, wherein the ultrasounds in thefirst range of frequencies and the ultrasounds in the second range offrequencies are transmitted according to a predetermined sequence. 13.The vacuum-assisted resin transfer molding process as claimed in claim11, wherein the ultrasounds are transmitted through the mold.
 14. Thevacuum-assisted resin transfer molding process as claimed in claim 11,wherein the mold comprises at least one ultrasound transducer mountedthereto or embedded therein.
 15. The vacuum-assisted resin transfermolding process as claimed in claim 11, wherein the process furthercomprises degassing at least one region of the resin-infused reinforcingmaterials.
 16. The process as claimed in claim 1, wherein theultrasounds in the first range of frequencies and the ultrasounds in thesecond range of frequencies are transmitted at different times accordingto a predetermined sequence.
 17. The process as claimed in claim 1,wherein the ultrasounds in the first range of frequencies and theultrasounds in the second range of frequencies are transmitted atdifferent power levels according to a predetermined sequence.
 18. Theprocess as claimed in claim 6, wherein the process further comprisesbleeding at least one region of the matrix-infused reinforcing materialsvia at least one degassing port located on the vacuum bag.
 19. Theprocess as claimed in claim 6, wherein the process further comprisesbleeding several regions of the matrix-infused reinforcing materials viaseveral degassing ports located on the vacuum bag.
 20. Thevacuum-assisted resin transfer molding process as claimed in claim 11,wherein the ultrasounds in the first range of frequencies and theultrasounds in the second range of frequencies are transmitted atdifferent times according to a predetermined sequence.
 21. Thevacuum-assisted resin transfer molding process as claimed in claim 11,wherein the ultrasounds in the first range of frequencies and theultrasounds in the second range of frequencies are transmitted atdifferent power levels according to a predetermined sequence.
 22. Thevacuum-assisted resin transfer molding process as claimed in claim 11,wherein the process further comprises bleeding at least one region ofthe resin-infused reinforcing materials.